如何使用Django的ORM拉一个随机记录？ [英] How to pull a random record using Django's ORM?

问题描述

我有一个模型，代表我在我网站上出现的绘画。在主要网页上，我想展示其中的一些：最新的，大多数时间没有访问的，最受欢迎的和随机的。

我正在使用Django 1.0.2。

虽然前3个容易使用django模特儿，最后一个（随机的）让我有些麻烦。我可以在我的视图中对它进行编码，如下所示：

  number_of_records = models.Painting.objects.count（）
 random_index = int（random.random（）* number_of_records）+1 
 random_paint = models.Painting.get（pk = random_index）
  

它看起来不像我想要的东西 - 这完全是数据库抽象的一部分，应该在模型中。另外，在这里我需要处理已删除的记录（然后所有记录的数量都不会覆盖我所有可能的关键值），并且可能还有很多其他的东西。

任何其他选项，我可以如何做，最好是在模型抽象的内部？

解决方案

使用 order_by '？'）将在生产的第二天杀死数据库服务器。一个更好的方法就像在从关系数据库获取随机行。

  from django.db.models.aggregates import count 
 from random import randint 
 
 class PaintingManager（models.Manager）：
 def random（self）：
 count = self.aggregate（count = Count（'id'））['count'] 
 random_index = randint（0，count  -  1）
 return self.all（）[random_index] 
  

I have a model that represents paintings I present on my site. On the main webpage I'd like to show some of them: newest, one that was not visited for most time, most popular one and a random one.

I'm using Django 1.0.2.

While first 3 of them are easy to pull using django models, last one (random) causes me some trouble. I can ofc code it in my view, to something like this:

number_of_records = models.Painting.objects.count()
random_index = int(random.random()*number_of_records)+1
random_paint = models.Painting.get(pk = random_index)

It doesn't look like something I'd like to have in my view tho - this is entirely part of database abstraction and should be in the model. Also, here I need to take care of removed records (then number of all records won't cover me all the possible key values) and probably lots of other things.

Any other options how I can do it, preferably somehow inside the model abstraction?

解决方案

Using order_by('?') will kill the db server on the second day in production. A better way is something like what is described in Getting a random row from a relational database.

from django.db.models.aggregates import Count
from random import randint

class PaintingManager(models.Manager):
    def random(self):
        count = self.aggregate(count=Count('id'))['count']
        random_index = randint(0, count - 1)
        return self.all()[random_index]

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